Effects of septal lesions on latent inhibition and habituation of the orienting response in rats.

In Experiment I, the latent inhibition effect; i.e., retardation of conditioned response acquisition when a previously presented but not reinforced stimulus is subsequently used as the conditioned stimulus, was investigated in normal and septal-lesioned rats. Normal animals subjected to 30 nonreinforced CS presentations prior to CS-shock pairings, were retarded in active avoidance acquisition compared to normal animals given no nonreinforced CS presentations. The same manipulation failed to produce such a difference in septal-lesioned rats. In Experiment II, while drinking, thirsty normal and septal-lesioned rats were exposed to the same stimulus which served as CS in Experiment I. The course of suppression of on-going drinking was used as a measure of orienting response habituation. Since no differences in habituation were found between normal and septal-lesioned subjects, the deficiency of septal-lesioned rats in latent inhibition cannot be due to impairment of orienting response habituation. These results, in addition to other septal deficits, were discussed with respect to a theory of septal deficiency which suggests that septal lesions result in an impairment in situations which involve a discontinuity of response and reinforecement.